1. Field of the Invention
This invention concerns partially dehydrated natural leavening barms. More particularly, it concerns those leavening barms which contain a non-maltose-fermenting Saccharomyces species and a maltose-fermenting Lactobacillus species as the majority microorganisms. These microorganisms are admixed with whole grain flour, most usually rye or wheat flour and water. The microorganisms in these barms are optionally further stabilized in the dried product by the inclusion of malted whole grain flour, an emulsifying agent and an antioxidant; the latter two both being obtained conveniently from soybean oil. These barms can bring about fermentation and natural leavening in breads and like baked goods. In addition, this invention relates to the method for producing these leavening barms in a granulated dried form and their use in a dried form for producing breads.
2. Description of Background Art
Some traditional leavening agents for breadmaking which are made from the grains wheat, rye, barley and oats and which may still be in use, are perpetuated by refreshing a portion of the leavening agent with flour, water and various other ingredients at intervals, between baking times. Usually these traditional leavening agents are not produced in a dried form for storage but instead must be continually refreshed to maintain the supply or restarted, with the risk that a useful culture may not be produced again. An exception to this may be the manner in which a sourdough leavening is dried in Finland. This is described by Oura, 1982, where he states that "A traditional way of preserving rye sourdough in Finland has involved the natural drying of the dough on the surface of wooden containers (Oura et al., "Breadmaking" in Fermented Foods, Rose ed., 1982, Academic Press, p. 134). From a practical point of view, there is an art to the drying process if the sourdough is to be rehydrated to an exactly similar sourdough, and that art is not described in the literature as far as can be ascertained at this time.
The microorganisms in several of these traditional leavening agents and one recently discovered leavening agent, have now been described (Oura et al., supra; Kouhestani et al., "Composition and Preparation of Iranian Breads," in Journal of the American Dietetic Association (1969) 55:262-266; U.S. Pat. No. 4,666,719) and a pattern is recognizable. The pattern of the microflora in the leavening agents of interest here is that they contain a Saccharomyces yeast species which does not ferment maltose together with a Lactobacillus species that does ferment maltose. The Saccharomyces yeast and the Lactobacillus are probably symbiotic and each will allow the other to grow well in the dough. These are the most usual majority microorganisms present but there are often minor amounts of other yeasts and bacteria which determine the more subtle characteristics of a particular leavening agent. Other yeast genera which have been recognized in continuous traditional leavening agents include Pichia and Hansenula. Other bacterial types which have been found in continuous leavening agents include Leuconostoc, Streptococcus and Pediococcus.
A currently accepted taxonomic classification of the Saccharomyces genus of yeasts (Yarrow, "Genus 22, Saccharomyces Meyen ex Reess," in The Yeasts. Kreger-van Rij ed. (1984), Elsevier Science Publishers BV, Amsterdam, pp. 379-395) includes seven species. There are three Saccharomyces yeasts that do not usually ferment maltose and which have been definitely recognized as useful in leavening agents; these are S. exiquus, S. telluris, and S. dairensis. S. exiquus is present in the San Francisco sourdough leavening where it grows symbiotically with Lactobacillus sanfrancisco (Oura, supra, p. 130) and also in Italian panettone dough (Oura, supra, p. 131) where it is found growing with Lactobacillus brevis and Lactobacillus plantarum. All these Lactobacillus species ferment maltose. S. exiquus has also been isolated from traditional Iranian bread dough (Tadayon, "Identification of Yeasts Isolated from Bread Dough of Bakeries in Shiraz, Iran," in Journal of Food Protection (1978) 41:9, pp. 717-721) in a study that was not concerned with any Lactobacillus species that might also have been present, so its symbiotic pairing there is not yet known.
S. telluris has been found in traditional bread doughs in Iran (Tadayon, supra) but without reference to a symbiotic pairing with a Lactobacillus species.
S. dairensis has been found in both wheat and rye leavening barms prepared from microorganisms to be found naturally occurring on the wheat or rye grain. In the wheat leavening barm S. dairensis appears to be growing symbiotically with an atypical strain of Lactobacillus brevis which nevertheless does ferment maltose (U.S. Pat. No. 4,666,719).
S. servazzii and S. unisporus are not mentioned yet in the literature as species useful for breadmaking even though they do not normally ferment maltose and would apparently be suitable for symbiotic pairing with a maltose-fermenting Lactobacillus species in a leavening agent. It is reasonable to expect that they will eventually either be used for breadmaking in conjunction with Lactobacillus species or they will be found to be present in some traditional bread leavening agents.
S. cerevisiae and S. kluyveri can usually ferment maltose and are not therefore suitable for symbiotic pairing with a Lactobacillus species which also ferments maltose. S. cerevisiae strains are used as modern bakers' yeast and S. kluyveri has been found in traditional leavening agents used to make bread in Iran (Tadayon (1978), supra). Breads made with either of these two yeasts would not be expected to have the characteristic flavor or self-preservative properties associated with the acids produced by symbiotic Lactobacillus bacteria present in the leavening agent.
The Lactobacillus species most usually found in sourdough leavening systems are L. plantarum, L. brevis, and L. fermentum (Oura, supra. p. 128). Other Lactobacillus listed in the most recent edition of Bergey's Manual (Kandler & Weiss, "Regular Nonsporing Gram-Positive Rods," in Bergey's Manual of Systematic Bacteriology," Vol. II, ed. Holt, Williams & Wilkins, Baltimore (1986), pp. 1208-1234) which have been isolated from sourdoughs are: L. farciminis, L. alimentarius, L. casei and L. sanfrancisco. Each of these species of Lactobacillus could be expected to be found growing symbiotically with one of the non-maltose fermenting Saccharomyces yeast. The specific pair that would grow naturally in a certain flour-and-water system would be determined by the nutrients to be found there. Examples of other leavening agents containing Lactobacillus species include those used to make German rye breads, and Egyptian and Iranian wheat breads (Oura, supra, p. 126; Faridi, "Flat Breads," in Wheat: Chemistry and Technology, Vol. II, ed. Pomeranz, 1988, American Association of Cereal Chemists, St. Paul, Minn., p. 479).
Isolation of the majority microorganisms only, and their subsequent perpetuation and use to inoculate a bread dough, may not produce the same characteristics obtainable from the original leavening agent. In order to preserve all the microorganisms that give the full character to traditional leavening agents and to make these traditional leavening agents more generally available, it would be useful to be able to prepare them economically in a storage-stable, dried, granular form, and then to be able to reproduce the original leavening agent easily from this form. Initial work showed that the seemingly obvious method of directly drying a mature leavening agent in the form of an extruded dough was uneconomical in energy use and in any case the microorganisms did not survive the process well.
Traditional leavening agents have been propagated through the centuries or restarted using ancient techniques, and until the nineteenth century, most likely with similarly grown and milled flour and a similar water supply.
Before the invention of roller milling in the nineteenth century a refined flour meant a finely ground flour containing parts, and therefore nutrients, from the whole grain. With the use of roller milling, a refined flour can be made which contains only the endosperm of the grain and practically none of the nutrients to be found in the germ and bran of the whole grain. The reduced number of nutrients present in modern roller-milled, refined flour is partially compensated for with added vitamins and minerals, to an extent that is varied from one country to another.
The grain variety selected for producing a modern flour may also be changing with time. Reasons for this are the development of new grain varieties and trading practices that result in the use of introduced varieties of grains from different areas of the world. A modern miller is likely to blend a series of different grain varieties, from several sources, into the flour which is finally sold.
Modern growth, storage and distribution condition for grains are almost certain to include the use of pesticides or a physical treatment to prevent insect or microbial contamination. Unfortunately, this same treatment probably also results in a loss of the microorganisms from which a traditional natural leavening could be made.
Before the use of roller milling, the finely ground flours were essentially whole grain flours which could not be stored for long periods without becoming rancid or being damaged by insects or moulds. Instead, the grains were stored whole and in general were milled only when they were about to be used for breadmaking. With this practice there was the additional advantage that those nutrients which might have been lost during even a short storage time were still available for the leavening microorganisms, as well as for those people eating the resulting bread.
The use of malted grains in bread doughs is a modern as well as an ancient practice. Malted grains add vitamins to the leavening or dough and enzymes that have a variety of activities including the improvement of the bread texture, the release of maltose from flour, and the breakdown of phytic acid and the resultant release of bound minerals for digestion. This activity provided by malted grains is due to the sprouting of the grain which is the second stage in the malting process following soaking in water. Subsequent processing during malting involves drying under conditions that determine the final malt properties; some enzymes are easily destroyed by heat while the malt is dried. In ancient times sprouting could have occurred while grains were being soaked in an attempt to soften them before making a dough, or the grains could have sprouted even before they were harvested, in rainy harvest seasons, and then been dried again while still in the ear of the grain. In other words, traditional leavening agents are most likely best supplemented with a simple malt rather than a refined sugar when it is desired to boost the growth of the leavening microorganisms.
The water available now for breadmaking is quite likely to have been treated with bacteriostatic chemicals. This is invaluable for preventing the spread of disease-causing microorganisms. However, if these chemicals remain in the water that is to be used for traditional breadmaking, then the proliferation of the natural leavening microorganisms may be impaired.
All of this is to say that in order to successfully produce and propagate a particular traditional leavening agent, it is necessary to use the whole grain flour from a particular variety of the grain, some of which has been sprouted or malted, and which has not been treated physically or with pesticides so as to destroy residual microorganisms and yet is nevertheless clean and undamaged, and to use a good drinking water that does not contain residual bacteriostatic chemicals. A leavening agent produced with these criteria is most likely to contain robustly growing microorganisms. Such a system would give the best leavening and would also have the best chance of surviving further processing such as drying for prolonged storage stability.
When all these criteria are met and the leavening agent is seen to contain a non-maltose-fermenting Saccharomyces species and maltose-fermenting Lactobacillus species as the majority leavening microorganisms, then perhaps this leavening could be classified as a "barm". In this way it would be distinguishable from sourdough starters which are often made with refined flours and sugars and are frequently used only to produce an acidic dough which is then leavened with S. cerevisiae in the form of bakers' yeast. A barm would be expected to produce a well-acidified dough and the corresponding characteristics in the finished bread. A sourdough leavened with bakers' yeast might produce only a partially acidified dough since the yeast would most likely ferment the same sugars as the acidifying bacteria, and so prevent their full proliferation.
The desirability of producing leavening barms is partly due to the concept of continuing an ancient art successfully, but more important are the properties of the whole grain breads produced. The acidic doughs of barm breads result in good flavor for the finished bread, self-preservation against the growth of molds, and enhanced availability for digestion, even over the effect of malted grain or simple bakers' yeast fermentation, of the minerals naturally present in the whole grain flours (Faridi, supra, p. 496).
A particular leavening barm containing the symbiotic microorganisms, Saccharomyces dairensis and Lactobacillus brevis, admixed with water and whole grain flour in the form of a slurry, paste or dough is now known and is described in U.S. Pat. No. 4,666,719 of Spiller. This barm has a limited storage life. When this barm is held at about 4.degree. C., it remains useful as a leavening agent for about two months after preparation. At room temperature, the barm has a shorter shelf life--on the order of several days. While this barm is quite useful, it would be advantageous to have the barm in a form which would permit it to be distributed and stored for long periods without the cost and inconvenience of refrigeration. This would make the barm potentially more universally available. This invention provides for barms such as this in a dried or granulated form.
Economically feasible methods for producing dry baker's yeast and dried bacterial cultures separately are known, but methods for economically drying symbiotic yeast and bacterial pairs in the presence of whole grain flour are not known to be in use. Baker's yeast (Saccharomyces cerevisiae ) strains have been available in dry forms stable at room temperature, since the 1920's. Some bacteria are also generally associated with dried forms of baker's yeast but they are neither intended nor expected to multiply appreciably in the dough as part of a desirable fermentation.
References to the production, stability and use of dried forms of baker's yeast are made in Reed & Peppler, Yeast Technology, 1973, AVI Publishing Co., Westport, Conn., pp. 90-102, 139-147; and by van Dam, "The Biotechnology of Baker's Yeast", in Chemistry & Physics of Baking ed. Blanshard et al., 1986, Royal Society of Chemistry, London, pp. 117-131. These references are believed to well summarize the state of the art. The most usual active dry yeast has a moisture content of between 7.5% and 8.3% and can remain viable at ambient temperatures for a year if it is stored under nitrogen or vacuum. Over that period only about 10% of its activity is lost. Its particular stability is due to factors such as its low moisture content, the addition of emulsifiers, antioxidants and soybean oil in some cases and to the selection of specific strains of Saccharomyces cerevisiae that survive the dehydration process well. However, the water used for the rehydration of active dry yeast for breadmaking must be at 40 .degree. C. to avoid excessive leaching of the yeast cell contents and subsequent loss of leavening activity and damage to the gluten. When the moisture content of baker's yeast is below 7.5%, water vapor rehydration is necessary to prevent loss of leavening activity.
Two patent references are of particular interest because use is made of flour in producing dried forms of bacteria and yeast. One is U.S. Pat. No. 4,243,687 issued to Kline, for the preparation of a freeze-dried natural sourdough starter. Flour forms part of the supporting medium on which the starter is freeze-dried but the conditions do not allow the symbiotic yeast in the starter to survive the drying process. The end product is a dried form of Lactobacillus sanfrancisco in a mixture containing a refined wheat flour. U.S. Pat. No. 3,510,312 issued to Rupprecht and Popp is also of importance here, since it is concerned with the drying and resultant stabilization of baker's yeast with various pre-dried flours. A final moisture content of 11-15% in the baker's yeast mixture is achieved in this process, and provides a mixture which can be used satisfactorily for baking after several months storage at room temperature.
Johnston in U.S. Pat. No. 2,919,194, describes a method for suspending compressed yeast in oil and performing the dehydration while the yeast is in contact with the oil. The excess oil is removed at the end of the drying process and the dried yeast produced still contains 5-10% oil unless it is removed with a solvent. The presence of a wetting agent such as lecithin is recommended as advantageous by Johnston as is the presence of a yeast fermentable saccharide. (The corn oil used by Johnston may have been a less refined oil, and thus contained significant amounts of lecithin, since he makes no mention of using a refined corn oil.) It is also important to note that Johnston recommended prior propagation of the yeast in a medium somewhat reduced in phosphorus and nitrogen. This dehydration method has the reputation of producing a very stable and effective dried yeast, but the process was found to be too expensive to bring into general use. However, instant dried yeasts are today being produced that are admixed with polyglycerol esters of fatty acids, potato starch and soy bean oil which is also an oil known to contain significant amounts of the emulsifying agent lecithin, as well as antioxidant tocopherols, provided it has not been refined.